By percentage of GDP given as development aid, US is ranked 19th.
For some reason, crazy Scandinavian socialist countries are more generous than god fearing free-market capitalizt 'Merrica... Go figure.

I'm assuming you must be referring to the 1950s, when the highest marginal tax rate in the country was 91%. (if I'm not mistaken) The difference is, that rate kicked in at a much higher dollar amount than today's 38% percent does. Plus, there were many more loopholes for people to avoid excessive taxation through. No one with a pulse willingly gives the government 91% of their money. In the 80's taxes were lowered across the board and simplified somewhat. God knows how complex they must have been beforehand, because they still aren't "simple".